Biomass that is organic resources of biological origin is produced by living organisms from water and carbon dioxide by the use of solar energy, and is sustainable and renewable resources. In recent years, as a part of global warming countermeasures, attempts have been extensively made to produce ethanol from biomass that contains a cellulosic material such as woody biomass or herbaceous biomass, and to use the ethanol as various types of fuel or chemical materials. Biomass ethanol produced from the biomass is a renewable natural energy, and the amount of carbon dioxide released into the condition does not increase even if the biomass ethanol is burned. From these perspectives, biomass is attracting attention as available and effective resources and is expected to be used as future energy sources.
The biomass is a collection of living organisms incorporated into the material circulation system in the earth's biosphere or a collection of organic matters derived from the living organisms (see JIS K 3600 1258). For example, the biomass is classified into a forest/woodland type (lumber scraps, lumber from thinning, paper waste and the like), an agricultural type (rice straw, wheat straw, sugarcane residues, rice bran, palm shell, plants and the like), an animal type (domestic animal waste and the like), a fishery type (fish processing residues and the like), and a waste type (left-over food products, garden plants, construction waste, sewerage sludge and the like).
Conventionally, as an ethanol producing method, there is used an ethanol producing method that includes saccharifying biomass or the like that contains a carbohydrate-based material, a cellulosic material or the like to produce a saccharide solution, and fermenting the obtained saccharide solution, thereby producing ethanol. For example, as an ethanol producing method using biomass, the following methods are proposed: an ethanol producing method that includes hydrolyzing collected biomass into saccharides by the addition of sulfuric acid, performing thereafter solid-liquid separation, neutralizing a liquid phase, subjecting the neutralized liquid phase to ethanol fermentation using microorganism such as yeast, and converting the liquid phase into ethanol (see Patent Literatures 1 and 2); and an ethanol producing method that includes performing hydrothermal decomposition by causing collected biomass and pressurized hot water to contact each other in a consolidated condition, thereby obtaining hydrothermally treated biomass, adding enzyme to the obtained hydrothermally treated biomass and saccharifying the obtained hydrothermally treated biomass, thereby obtaining a saccharide solution, and fermenting the obtained saccharide solution, thereby producing ethanol (see Patent Literatures 3 and 4).